1. Field of the Invention
The present invention relates to organic electroluminescent panels and production methods thereof, and color filter substrates and production methods thereof. More specifically, the present invention relates to an organic electroluminescent panel preferable for large and full-color panels, a production method thereof, an organic electroluminescent display device, a color filter substrate, a production method thereof, a liquid crystal display panel, and a liquid crystal display device.
2. Description of the Related Art
Organic electroluminescent (hereinafter, also referred to as “EL”) displays have been drawing attention as a next generation flat panel display (FPD) because such displays are excellent in visibility such as contrast and viewing angle and responsivity and permits low power consumption, slim profile, light weight, and flexibilization of the displays themselves. Such organic electroluminescent displays are still inferior to liquid crystal displays (LCD) or plasma display panels (PDP) in technical completeness or standard of industrial infrastructure. Therefore, practical use of the organic EL displays is still only loading on car audios or some mobile information devices. However, the organic EL displays are theoretically the most excellent FPDs and therefore, future market expansion is expected for the displays.
Such organic EL displays display images by driving an organic EL panel having a configuration in which a light-emitting organic EL element is disposed in every pixel. The organic EL element has a structure in which an organic layer including a luminescent layer is interposed between a pair of electrodes at least one of which has transparency. Small molecular organic (EL) materials have been used in the organic layer of the organic EL element because luminescent principle in small molecular organic materials was first found. A production process flow of a passive matrix (PM) driving organic EL panel using a small molecular organic material was disclosed (for example, referring to E Express ed., “E de miru yuki EL display no seizo process 03”, E Express Inc., 2003, CD-ROM (Nonpatent Document 1)) . A vapor deposition method of subliming a material in a vacuum and depositing the material on a substrate, thereby forming a film, is generally used for film-formation of the small molecular organic materials.
FIG. 6 is a planar view schematically showing a structure of a currently used PM driving type organic EL display device before formation of an organic layer. FIG. 7 is a cross-sectional view schematically showing the organic EL display device taken along line d-d′ in FIG. 6. R, G, and B in FIG. 6 represent a red pixel, a green pixel, and a blue pixel, respectively.
In the organic EL display device shown in FIG. 6, as shown in FIG. 7, a linear insulator made of two different insulating films, that is, an edge cover (insulating layer) 51 and a cathode separator 52, are formed on a lower electrode (anode) 50, and fine patterning of a cathode, or coating separation of an organic thin film at the time of deposition can be permitted. A configuration of an organic EL element in which a half tone pattern serving as the edge cover and an insulating layer serving as the cathode separator are formed in one layer for simplification of production steps and the like was disclosed (for example, referring to Japanese Kokai Publication No. 2003-100466 (pages 2, 12, and 14, FIG. 3)(Patent Document 1)).
Growth in size of panels has been recently needed also for the organic EL display devices as well as for various FPDs.
Problems associated with the growth in size include (I) a driving system of the pixel and (II) a film forming method of the organic layer.
As for (I), increase in the number of pixels associated with the growth in size delays a response speed or causes crosstalk by signal interference between the pixels in the PM driving type. On the other hand, the active matrix (AM) driving type that drives each pixel independently does not cause the above-mentioned defects, and therefore, the AM driving type is preferable as a system of driving pixels in a large panel. However, the AM driving type has more portions where the upper electrode and the bank are stacked, in comparison to the PM driving type in which the upper electrode is formed in a stripe pattern over the entire surface as an electrode that is common for all of the pixels. Therefore, discontinuity (physical and electrical separation caused by the step) of the upper electrode tends to occur at the boundary between the bank and the lower electrode. In this respect, there was room for contrivance.
As for (II), a vapor deposition technique is generally used in formation process of an organic layer in organic EL panels using small molecular organic materials. Therefore, film unevenness is likely to be generated in a large area panel, and production costs are high. Therefore, no technical prospect of production process for large panels has yet emerged. Due to the above circumstances, polymer organic (EL) materials have been noted as a material for organic layers. The polymer organic materials can be dissolved in a solution (solvent) and therefore formed as a film by wet processes such as a cast method, a spin coat method, and an ink jet printing method. The ink jet printing method is particularly preferable as an organic layer film-forming method in a large panel because the film thickness unevenness in a large panel can be reduced and higher definition of display by coating separation at the time of application, reduction in materials, and improvement in yield can be attained. However, if the ink jet printing method is used, overflow and pull-in of the ink may cause color mixing between pixels. In such a respect, there was room for contrivance. Neither the above-mentioned Nonpatent Document 1 nor Patent Document 1 studied the above-mentioned (I) and (II).
FIG. 8 is a planar view schematically showing a configuration of a conventional active matrix (AM) driving full-color organic EL panel. R, G, and B in FIG. 8 represent a red pixel, a green pixel, and a blue pixel, respectively.
In the organic EL panel shown in FIG. 8, a bank 62 is formed to have a height t1 enough to prevent discontinuity of an upper electrode (not shown) . However, the bank 62 having a height (thickness) of t1 has a low capability of keeping the ink inside the bank, and for example, the ink applied in the pixel region of G (green) flows into adjacent pixel regions of R (red) and B (blue), and thereby a color mixing defect is more likely to be generated. This can be prevented by reducing the ink amount applied (pooled) per ejection. However, in order to obtain a film thickness needed for obtaining desire luminescent characteristics (luminescent efficiency, lifetime), the number of times the combination of application and drying is repeated needs to be increased, which increases the number of steps of forming the organic layer. In such a respect, there was room for improvement. On the other hand, if a bank 62 having a height of t2 enough to keep the ink is formed, the capability of keeping the ink can be secured, but the discontinuity of the upper electrode is likely to occur near the boundary between the lower electrode 61 and the bank 62, and electrically-separated pixels (dots) due to the discontinuity are not lighted. In such a respect, there was room for improvement.
Also for liquid crystal displays in addition to the organic EL displays, the growth in size is needed. Therefore, even in formation of a colored layer of a color filter substrate for liquid crystal displays, application of the wet processes such as the ink jet printing method has been investigated. Therefore, even in preparation of the color filter substrate, it has been needed that color mixing between adjacent pixels, caused by overflow or pull-in of a liquid material, or discontinuity of an upper electrode is prevented.